1. Field of the Invention
The invention is directed to an improved fuel injection apparatus for an internal combustion engine.
2. Description of the Prior Art
A fuel injection apparatus of the type with which this invention is concerned is known from WO 01/40656 A and has a high-pressure pump that delivers fuel into a reservoir from which fuel is drawn for injection into the engine. In addition, a fuel-supply pump is provided, which supplies fuel to the high-pressure pump from a fuel tank. The high-pressure pump has a housing and at least one pump element that is driven by a drive unit disposed in an internal chamber of the housing. The pump element has a pump piston, which is set into a stroke motion by the drive unit and delimits a pump working chamber. During an intake stroke of the pump piston, it draws fuel into the pump working chamber via an inlet and during a delivery stroke of the pump piston, it displaces fuel from the pump working chamber via an outlet. The pump piston moves into the internal chamber of the housing during its intake stroke and moves out from the internal chamber during its delivery stroke. The fuel-supply pump can be electrically or mechanically driven. In order to be able to generate a sufficiently high pressure, the fuel-supply pump requires a high-output, correspondingly costly drive unit. Alternatively, it is also possible for a fuel-supply pump with a low-output electric drive unit to be combined with an additional fuel-supply pump with a mechanical drive unit, but this is also costly.
The invention is based on a fuel injection apparatus for an internal combustion engine as generically defined by the preamble to claim 1.
A fuel injection apparatus of this kind is known from WO 01/40656 A. This fuel injection apparatus has a high-pressure pump that delivers fuel into a reservoir from which fuel is drawn for injection into the engine. In addition, a fuel-supply pump is provided, which supplies fuel to the high-pressure pump from a fuel tank. The high-pressure pump has a housing and at least one pump element that is driven by a drive unit disposed in an internal chamber of the housing. The pump element has a pump piston, which is set into a stroke motion by the drive unit and delimits a pump working chamber. During an intake stroke of the pump piston, it draws fuel into the pump working chamber via an inlet and during a delivery stroke of the pump piston, it displaces fuel from the pump working chamber via an outlet. The pump piston moves into the internal chamber of the housing during its intake stroke and moves out from the internal chamber during its delivery stroke. The fuel-supply pump can be electrically or mechanically driven. In order to be able to generate a sufficiently high pressure, the fuel-supply pump requires a high-output, correspondingly costly drive unit. Alternatively, it is also possible for a fuel-supply pump with a low-output electric drive unit to be combined with an additional fuel-supply pump with a mechanical drive unit, but this is also costly.